Objectives: 1. Relation of radiosensitivity to chromatin mass/cell, between species: By collection of data on radiosensitivity (Do, LD/50) to chromatin mass/cell from a number of species, we will test whether this measure of genomic size, chromatin mass/cell, is a better predictor of radiosensitivity, between species, than the presently utilized nuclear volume or DNA/cell parameters. Chromatin mass/cell values will be obtained directly, by analysis from purified chromatin, or indirectly via NV and DNA/cell data. 2. Radiation damage to capillary circulation: Using microangiographic methods, we will measure damage to capillary circulation in mice, and compare acute- with fractionated-exposure damage, and damage in small intestine with that in kidney. 3. Ozone effect: We will measure chromosome breakage in vivo in hamsters breathing ozone in air at measured levels, and compare with breakage from known radiation levels. Blood cultures from exposed animals, with chromosomal analysis from leukocyte slides will be made. Lung tumors from ozone exposure will be looked for.